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What does it mean for a chemical reaction to do work on a battery?

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#1
Apr29-12, 07:56 PM
P: 6
Hi everyone!

I basically understand how the materials used in the chemical reaction of a battery work but now I want to know why some batteries have different ratings of voltage.

From what I've read, this depends on the materials that are used. What does it mean for some materials to do more work on the charges in the battery? Does this just mean that the chemicals are talking more electrons from the cathode and supplying more electrons for the anode? I guess my real question is what is the difference between a 1.5v battery and a 1.25v battery? I'm not looking for a short answer like "It's just the materials used in the battery." I'm looking for an answer of how those materials affect the charges and how that affects the voltage and how the "chemistry" of the battery affects the "physics" of the battery.

Thanks for all your help!
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Mathesaurus
#2
Apr29-12, 08:17 PM
P: 3
I don't know how much chemistry background you have, so if this is either too confusing or not specific enough, please tell me.

Different chemicals (usually metal ions) have different "standard reduction potentials." This basically means that it takes different amounts of energies to add electrons to it, and depend on how strongly electrons in each species are attracted to their nuclei.

[Example table of Standard Reduction Potentials]

If you have a look at the table, you'll see that some species really "like" to gain electrons, while others don't. The more positive they are, the more likely they are to be reduced (gain electrons), while the really negative ones are likely to be oxidised (lose electrons).

A battery basically puts one chemical that oxidises easily on one side, and a chemical that reduces easily on the other. The chemical that oxidises keeps losing electrons, while the chemical that reduces accepts them.

Now, back to that table - the voltage of a battery depends on the difference in standard reduction potential between the chemicals used. Find the two chemicals in a battery on one of those tables and subtract them: the absolute value of that answer is the voltage of your battery.

Basically, the battery's voltage depends on how easily your chosen chemicals oxidise or reduce. If redox reactions happen easily, then the voltage is higher.


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